1. Field of the Invention
The embodiments described herein relate generally to a method and system for characterizing a substance and, more particularly, to a method and system for deriving a molecular interference function (MIF) of a liquid, amorphous substance, or gel from an X-ray diffraction (XRD) profile of the material.
2. Description of Related Art
Many known security systems for screening materials include a substance identification system that is configured with x-ray beam detection technology employing known x-ray diffraction (XRD) devices and methods. Many of these known XRD devices include at least one x-ray source to generate a single x-ray beam having a predetermined range of photon energies. Such security systems generate a diffraction profile of each substance irradiated with x-rays. Because such materials typically have a known and discernible XRD signature, detection, and identification of contraband items and substances is facilitated.
Identification of liquid, amorphous substances, and gel substances, sometimes referred to as LAGs, in security screening relies in part on determining an associated molecular interference function (MIF) for each substance. This, in turn, depends on estimating an effective atomic number of a scatter sample, that is, the x-rays scattered from at least a portion of an irradiated sample. At least some known XRD screening systems use a High Energy Tip Region Analysis (HETRA) method. However, using HETRA methods, regions of the resultant XRD profile are determined at relatively high momentums to accurately determine the mean atomic number. In such high momentum regions of the XRD profile, the signal strength is relatively low compared to the associated photon noise in the same region. Therefore, the resultant low signal-to-noise ratio may contribute to a decrease in detection rates of contraband substances and an increase in false alarms, generating uncertain results. Moreover, a large percentage of liquids, amorphous substances, and gels encountered in air passenger luggage are water-based, that is, aqueous in nature. This is at least partially due to the ease with which water, sometimes referred to as a “universal solvent”, is typically mixed with a wide range of additive substances.